NiCo2O4 Nanowire Arrays Research Articles

Electron-interactive 1D porous vertical NiCo2O4 nanowire and 3D N-doped graphene aerogel enable high hydroxyl-ion adsorption capacity for superior energy storage

Supercapacitors are a kind of highly efficient energy-storage device with long cycle life and high power density, however, their specific capacitance is insufficient for further application and development. In this work, a novel composite with one-dimensional (1D) NiCo2O4 nanowire arrays (NiCo2O4-NWA) vertically supported on three-dimensional (3D) nitrogen-doped graphene aerogel (NGA) is designed and facilely realized by hydrothermal reaction and thermal treatment. The NiCo2O4 nanowires, with length of ∼1 μm and diameter of ∼25 nm, display a porous structure and are regularly arranged on both sides of the sheets in nitrogen-doped graphene aerogel. The aerogel-supporting NiCo2O4 nanowires demonstrate a remarkably high specific capacitance of 2742 F g−1 at 1 A g−1, and an outstanding cyclic stability with capacitance retention of 90% even after 10,000 cycles at 80 A g−1. The density functional theory calculation shows the narrow band gap (0.32 eV) and strong electronic interaction and hydroxyl-ion adsorption effect of NiCo2O4 supported on NGA, resulting in superior specific capacitance and energy storage performance. The 3D nitrogen-doped graphene aerogel supporting 1D nanowire arrays represent a promising high-performance electrode material for application in the supercapacitors and other electrochemical energy-conversion and storage equipment.

Facile synthesis of NiCo2 O4/rGO nanowire array electrodes for supercapacitor cathodes

In this study, NiCo2O4/rGO nanowire arrays (NWAs) were effectively synthesized, and these arrays were subsequently employed as components in supercapacitors. The phase structure of the materials was analyzed using X-ray diffraction spectroscopy, and the morphology of the materials was observed by scanning and transmission electron microscopy. By comparing with NiCo2O4 nanowire arrays without graphene oxide, it was found that the surface of NiCo2O4 arrays grown directly on nickel foams had a large number of accumulations, whereas the surface agglomerations of NiCo2O4/rGO nanowire arrays complexed with reduced graphene oxide were significantly improved. The NiCo2O4/rGO electrode with improved agglomeration phenomenon shows better performance. The specific capacitance of NiCo2O4/rGO NWAs is 2311 F·g-1 at 1 A·g-1 and remains at 1211 F·g-1 even at 50 A·g-1. In addition, the capacitance retention of this material could reach 83.5 % after 3,000 cycles at 10 A·g-1, demonstrating excellent multiplicative performance and cycling stability.

Fabrication and Electrochemical Analysis of NiCo2O4@Ni-MOF Nanoarchitectonics Composites on Ni-Foam Substrate for Supercapacitor Electrodes

To produce the free-standing electrodes, a binder-free direct growth method was employed for electrode fabrication. A NiCo2O4@Ni-MOF (metal–organic framework) composite was synthesized using a one-pot hydrothermal method. Initially, a NiCo2O4 nanowire array was cultivated on Ni foam, serving as a connecting bridge to ensure robust adherence of the Ni-MOF to the substrate. The structures of NiCo2O4 nanowire arrays exhibit the capacity for numerous redox reactions. Hybridizing MOF with transition metal oxide (TMO) nanoarchitectures can significantly alleviate the small specific surface area and aggregation tendency of TMOs. The highest energy storage capacity was obtained when the ratio of nickel to terephthalic acid (TPA) was 4:1. NiCo2O4@Ni-MOF (Ni:[Formula: see text]:1) exhibited a high storage capacitance of 1700[Formula: see text]F/g. The integration of MOF with TMO nanoarchitectonics as materials for supercapacitor electrodes can enhance porous structure and facilitate diffusion during both charging and discharging processes.

Research on 3D network in-situ grown NiCo2O4 nanowire arrays construction and its energy storage performance

In this paper, NiCo2O4 nanowire arrays are synthesized on 3D NF skeleton by a one-step hydrothermal method and used as anode materials for lithium-ion batteries (LIBs). Dense nanowire arrays are grown in situ on NF skeleton, cross-linked and constructed into 3D network structure. As an anode, it exhibits excellent electrochemical properties. The initial discharge capacity of NiCo2O4/NF is as high as 1316 mAh g−1 at a current density of 0.2 A g−1, and the specific capacity of 790 mAh g−1 can be maintained after 200 cycles. And NiCo2O4/NF can also maintain a specific capacity of 580.37 mAh g−1 at a current density of 1 A g−1 in the rating performance. And transfer resistance after 200 cycles reduced by 53.5%,which shows a tendency to decrease during the reaction process and accelerates the rate of Li+ transfer, improved battery cycling performance. The excellent lithium storage performance is attributed to the high aspect ratio of the nanowires themselves and the stable 3D network structure, which not only facilitates the rapid transfer of substances and diffusion of Li+, but also alleviates the volume change during the charge/discharge cycle. The band gap of NiCo2O4 can be obtained as 0.671 eV by first nature principle calculation, the electrons readily jump from the valence band to the conduction band and have good conductivity. And the diffusion potential barrier is 0.4 eV, which is easily overcome in the experiment and facilitates the transport of lithium ions.

Carbon fabric composites with NiCo compounds: Structure evolution and EMI shielding performance

NiCo layered double hydroxide (LDH) nanowire arrays (NWAs) were grown on carbon fabric (CF) via hydrothermal processes, then annealed into NiCo2O4 NWAs at 350 °C and finally melted into NiCo2 particles at 800 °C. The influence of such NiCo compounds on the electromagnetic interference (EMI) shielding performance of CF was investigated, and the results suggested that the LDH NWAs enhanced the microwave attenuation of CF, except for its shielding effectiveness (SE). In contrast, the NiCo2O4 NWAs with superior conductivity improved the SE of CF mainly via multiple reflections, while its shielding mechanism was essentially unchanged. Only the NiCo2 particles could basically improve the surface reflection of CF and enhance its internal absorption simultaneously. Consequently, the CF-NiCo2 composite showed a total SE of 52 dB, reflectivity of ∼0.92 and absorptivity of ∼0.08, better than 44 dB, ∼0.94 and ∼0.06 of CF, paving a new way for the fabrication of high-performance EMI shielding fabrics.

Pt/NiCo2O4 nanowire arrays on Ni foam as catalysts for efficient formaldehyde oxidation at room temperature

Catalytic oxidation of formaldehyde (HCHO) at room temperature is a low-cost and efficient solution for indoor HCHO removal. In this work, NiCo2O4 nanowires were in-situ synthesized on nickel foam (NF) by a simple hydrothermal reaction and then decorated with platinum nanoparticles (NPs). The Pt/NiCo2O4-NF catalyst exhibited excellent HCHO oxidation capacity at ambient temperature, realizing a conversion rate of 90 % within 60 min. The nickel foam substrate prevents the aggregation of NiCo2O4 nanowire arrays. It also enables the growth of large-area and aligned nanowires, contributing to the uniform dispersion of Pt NPs. Moreover, due to the unique redox property and high reactivity of NiCo2O4, numerous surface oxygen vacancies and active oxygen species are generated together with Pt by NaBH4 reduction, which is beneficial to the adsorption and oxidation of HCHO. Moreover, the hierarchical macro-/mesoporous structure of Pt/NiCo2O4-NF facilitates the diffusion of gaseous reactants and provides easily accessible active sites. In contrast with nanosized catalysts, the three-dimensional (3D) Pt/NiCo2O4-NF catalyst possesses high machinability and practicability. This work may shed light on the fabrication of 3D hierarchical catalysts for oxidative HCHO removal and indoor air purification.

Coupling Bimetallic NiMn-MOF Nanosheets on NiCo2O4 Nanowire Arrays with Boosted Electrochemical Performance for Hybrid Supercapacitor

As promising electrode materials for supercapacitors, metal-organic frameworks (MOFs) with rich porosity, large surface area and abundant redox sites have attracted increasing attention. Nevertheless, the intrinsically interior electrical conductivity and ease of agglomeration for most MOFs have largely restricted their energy storage application. In this work, we report the controlled fabrication of bimetallic NiMn-MOF nanosheets on the surface of NiCo2O4 nanowire arrays to form NiCo2O4@NiMn-MOF core-shell structure and investigate the effect of Mn incorporation in Ni-MOF shell on the electrochemical performance of the hybrid arrays in supercapacitors. Benefitting from the delicately designed structures and compositions, the optimal NiCo2O4@NiMn-MOF electrode presents an extraordinarily high specific capacity of 243.0 mAh/g at 2 mA/cm2. We further assembled a flexible solid-state hybrid supercapacitor with NiCo2O4@NiMn-MOF and activated carbon as electrodes, exhibiting a high energy density of 48.2 Wh/kg at 1606.7 W/kg, accompanied by excellent mechanical flexibility and electrochemical durability. This work demonstrates a new approach for developing novel MOF array-based electrode materials with boosted electrochemical performance in the field of flexible energy storage devices.

Multifunctional carbon fiber@NiCo/polyimide films with outstanding electromagnetic interference shielding performance

The electromagnetic interference (EMI) shielding materials with low reflection characteristics are highly desirable for integrated communication and microelectronics systems to shield EM waves and their secondary pollution. In this study, the EMI shielding materials with outstanding absorption performance were fabricated via the two-step pyrolysis and followed by vacuum assisted filtration approach. The chopped carbon fibers (CFs) wrapped with NiCo2O4 nanowire arrays (CF@NiCo2O4) were prepared by the hydrothermal reaction initially. After annealing, the NiCo2O4 nanowires transformed into NiCo alloy nanoparticles and evenly embedded in the CFs, endowing the CF@NiCo composites with efficient magnetic loss and dielectric loss capacity. After vacuum filtration and encapsulation with polyimide, the obtained flexible CF@NiCo/polyimide composite film displays superior EMI shielding effectiveness of 87 dB with a thickness of only 1.08 mm. Particularly, the composite film exhibits extremely low SER characteristics of ~6 dB, which surpasses those of most previously reported composites materials with similar thickness. In addition, the composite films present outstanding flexibility, mechanical properties and Joule heating performances. Therefore, the prepared flexible composite films have broad prospect for EMI shielding and thermal management applications in advanced microelectronic systems.

Rational construction of NiCo2O4@Fe2O3 core-shell nanowire arrays for high-performance supercapacitors

Fe2O3 electrode materials exhibit excellent electrochemical performance in electrochemical energy storage system. However, its poor electrical conductivity limits its future practical application. The binder-free NiCo2O4@Fe2O3 composites was reasonably designed and fabricated on carbon fiber paper with NiCo2O4 nanowires as conductive scaffold in the present investigation. The three-dimensional nanostructure of the porous Fe2O3 nanorods coated the NiCo2O4 nanowire arrays showed the fascinating electrochemical performance, including high specific capacitance of 262 ​mF/cm2 at a current density of 1 ​mA/cm2, and remarkable cycle stability with ~74.2% capacitance retention after 4000 cycles. The excellent pseudocapacitance performance of NiCo2O4@Fe2O3 composite materials is due to synergistic effect between NiCo2O4 and Fe2O3. The results of the present work show that NiCo2O4@Fe2O3 core-shell composite electrode is expected to exhibit excellent performance in the field of supercapacitors.

Porous NiCo2O4 Nanowire Arrays as Supercapacitor Electrode Materials with Extremely High Cycling Stability

In this work, NiCo2O4(NCO) was synthesized via microwave hydrothermal method and a further annealing treatment. Research results have shown that the surface defects(Co2+ site) and pore size of the materials can be adjusted by simply changing the calcination temperatures, and porous nanowire arrays structure can be obtained. The porous structure is conducive to the penetration of the electrolyte and enables the NCO to fully participate in the electrochemical reaction. What’s more, the NCO material has ample space to buffer the volume change in the cycle test, improving the cycling stability. The NCO obtained at 350 °C has better performance. It exhibits a specific capacitance of 648.69 F/g at 1 A/g and good rate capability. Especially, at 10 A/g, the specific capacitance can still be maintained at 80.00% after 10000 galvanostatic charge/discharge(GCD) cycles, showing excellent cycling stability.

Metal-organic framework derived directional growth of ultrathin amorphous NiCo hydroxide nanosheets on NiCo2O4 nanowire arrays for enhanced electrochemical properties

The rational design of hierarchical nanostructured electrode materials is critical for achieving high electrochemical property for supercapacitor (SC) applications. Herein, we report a facile method for fabricating hierarchical NiCoO@NiCo–OH core-shell nanowire array (NiCoO@NiCo–OH NWA) on flexible carbon fiber clothes by using a cobalt-based metal organic framework (Co-MOF) as an intermediate. The growth mechanism study shows the formation process is completed by a localized dissolution of Co-MOF followed by a directional growth of NiCo–OH nanosheets on NiCo2O4 nanowires. The unique hierarchical nanostructure endows the material a high surface area, rich active sites, fast electron transport, and efficient electrolyte ion diffusion. Consequently, the as-prepared material exhibited an over 3 times’ higher specific capacity than the pristine NiCo2O4 nanowire arrays and an excellent rate capability at 40 A g−1 for SCs. Moreover, the NiCoO@NiCo–OH NWA based hybrid supercapacitor (HSC) exhibited a considerably high energy density of 57.2 Wh kg−1, a high power density of 17.6 kW kg−1, and ultralong cycling stability of over 10 000 cycles (retention rate of 91.8%), outperforming most of the current state-of-the-art SCs. The directional growth strategy using MOFs as intermediates reported here provides a simple but effective way to fabricate hierarchical nanostructured electrode materials for advanced energy storage applications.

In situ formation of Co3O4 hollow nanocubes on carbon cloth-supported NiCo2O4 nanowires and their enhanced performance in non-enzymatic glucose sensing

Diabetes is a chronic disease that can seriously affect human health. Therefore it is important to develop a rapid and highly sensitive enzyme-free glucose sensor to aid the treatment of diabetes. In this work, homogeneous NiCo2O4 nanowire arrays were synthesized in an orderly fashion on flexible carbon cloth (CC) by a facile hydrothermal method. Then well-structured zeolitic imidazolate framework (ZIF-67) nanocubes were grown in situ on the as-prepared NiCo2O4 nanowires to form a hybrid nanoarchitecture. The hierarchical structure was transformed into a Co3O4/NiCo2O4/CC composite after annealing in the air. The as-prepared electrode was put into 0.1 M NaOH, and cyclic voltammetry and amperometry were employed to investigate its electrocatalytic properties at room temperature. It was found that the Co3O4/NiCo2O4/CC electrode exhibited outstanding sensing properties towards glucose, including terrific sensitivity (12.835 mA mM−1 cm−2), a wide linear range (from 1 μM to 1.127 mM), a low detection limit (0.64 μM) and a fast response time (within 2 s). In addition, it also had excellent selectivity, reproducibility and stability. The improvement in enzyme-free glucose sensing, in addition to the high porosity and large specific surface area of metal organic framework-derived Co3O4 hollow nanocubes, can be attributed to the NiCo2O4 nanowire arrays affording fast channels for electron transfer between CC and Co3O4. Accordingly, this method, which directly prepares hierarchical composite nanomaterials on a conductive substrate, may open up a new perspective for the enhancement of non-enzymatic glucose-sensing properties.

Ultrathin Ni-MOF nanosheet coated NiCo2O4 nanowire arrays as a high-performance binder-free electrode for flexible hybrid supercapacitors

Metal–organic frameworks (MOFs) as a kind of novel electrode material for energy storage has attracted increasing attention. However, their poor conductivity and difficulties in directly grown on the current collector largely thwart their maximum performance. Herein, an effective strategy was developed to increase the overall electrical conductivity and active surface area of MOFs by implanting conductive NiCo2O4 nanowires on carbon cloth as the interconnected anchors for in situ growth of MOFs nanosheets. The as-synthesized NiCo2O4@Ni-MOF electrode delivers an ultra-high areal capacitance of 7.23 F cm−2 at a current density of 5 mA cm−2, with an exceptional rate capability (5.04 F cm−2 at a very high current density of 30 mA cm−2). Meanwhile, NiCo2O4 NWAs are used as the strain buffer supports for preparing core−shell NiCo2O4@PPy nanorod arrays as a negative electrode. As a result, an HSC is successfully assembled by using the NiCo2O4@Ni-MOF and NiCo2O4@PPy as electrodes, achieving both high volumetric capacitance and energy density. This study presents a versatile strategy for effectively fabricating MOFs based binder-free energy storage materials for future portable and wearable electronic devices.

Hydrothermal synthesis of reduced graphene oxide-modified NiCo2O4 nanowire arrays with enhanced reactivity for supercapacitors

Supercapacitors have attracted great attentions for their excellent performance in the energy devices. In this work, the reduced graphene oxide (rGO) modified NiCo2O4 (rGO/NiCo2O4) are fabricated by a simple hydrothermal route. After the rGO modification, the sea urchin-like structure of NiCo2O4 was broken and the NiCo2O4 nanowires would intertwine with each other. Benefit from the large surface areas and the active sites of this unconsolidated structure, the as-prepared rGO/NiCo2O4 exhibited the excellent specific capacitance of 1003 F g−1 at the current density of 1 A g−1 and enhanced rate capability (89% from 1 to 10 A g−1). And the cycle stability could reach 57% retention after the 10000 cycles. The rGO/NiCo2O4 composite might hold great promise for future application of the high-performance supercapacitor.

NiCo2O4 nanowire arrays rich in oxygen deficiencies for hydrogen evolution reaction

The rational design of highly efficient electrocatalysts to generate hydrogen by catalyzing hydrogen evolution reaction still remains a challenge. Herein, we report a simple strategy to significantly enhance the catalytic activities of NiCo2O4 nanowire arrays by simply tuning the amount of oxygen vacancies. Remarkably, the oxygen-deficient NiCo2O4 catalysts obtained in Ar environment show significantly improved catalytic activities toward hydrogen evolution reaction with the requirement of 104 mV overpotential to afford 10 mA cm−2, 122 mV less than that for air-sintered NiCo2O4 (226 mV). Moreover, such catalysts also exhibit superior long-term durability for 24 h at 100 mA cm−2. The present study further promotes the application of NiCo2O4 in other energy storage and conversion system.

Interlaced NiMn-LDH nanosheet decorated NiCo2O4 nanowire arrays on carbon cloth as advanced electrodes for high-performance flexible solid-state hybrid supercapacitors.

The development of flexible energy storage devices for portable and wearable electronics has aroused increasing interest. In this work, three-dimensional hierarchical NiCo2O4@NiMn-LDH nanowire/nanosheet arrays have been successfully fabricated on carbon cloth through a facile hydrothermal and calcination synthetic method. Benefiting from the sophisticated hybrid nanoarchitectures with desirable structure and components, the optimized NiCo2O4@NiMn-LDH hybrid electrode is found to deliver a remarkable specific capacity of 278 mA h g-1 at 2 mA cm-2 and a good rate capability of 89.1% retention at 20 mA cm-2. Detailed analysis of the reaction kinetics for the hybrid electrode clearly indicates the dominant diffusion-controlled contribution to the total capacity. In addition, a flexible solid-state hybrid supercapacitor is assembled by taking NiCo2O4@NiMn-LDH and activated carbon as the cathode and anode, respectively, which manifests a maximum energy density of 47 W h kg-1 at a power density of 357 W kg-1 as well as an excellent long-term cycling stability (95.6% retention after 5000 cycles over 8 mA cm-2). Our work demonstrates the great potential of this core/shell hybrid nanostructure as an advanced battery-type electrode for high-performance flexible energy storage devices.

Hierarchical NiCo2O4 nanowire array supported on Ni foam for efficient urea electrooxidation in alkaline medium

NiCo2O4 nanowire arrays grown on Ni foam (NiCo2O4/NF) are synthesized by a simple template-free hydrothermal route followed by a thermal treatment in the air at 400 °C. The as-prepared Ni foam substrate exhibits homogeneous and porous nanowire arrays, which providing a number of active sites and electronic transmission channels for urea electrooxidation. The electroactivity of NiCo2O4/NF electrode toward the oxidation of urea in alkaline solution is evaluated using cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) measurements. Results show that the as-obtained electrode delivers an outstanding electrocatalytic activity and stability for urea electrooxidation. The NiCo2O4/NF electrode delivers a low open potential at 0.19 V versus Ag/AgCl with a corresponding current density of 570 mA cm−2 in 5 mol L−1 KOH and 0.33 mol L−1 urea electrolytes. Meanwhile, detailed investigation is made for the electrocatalytic oxidation of urea by varying several reaction parameters, such as scan rate, urea and KOH concentrations. Benefiting from the unique structure and synergistic effects of Ni and Co, the NiCo2O4/NF electrode exhibit superior electrocatalyst activity and is considered to be a promising candidate catalysis material for direct urea fuel cell.

Interface-Engineered Nickel Cobaltite Nanowires through NiO Atomic Layer Deposition and Nitrogen Plasma for High-Energy, Long-Cycle-Life Foldable All-Solid-State Supercapacitors.

The large-scale application of supercapacitors (SCs) for portable electronics is restricted by low energy density and cycling stability. To alleviate the limitations, a unique interface engineering strategy is suggested through atomic layer deposition (ALD) and nitrogen plasma. First, commercial carbon cloth (CC) is treated with nitrogen plasma and later inorganic NiCo2 O4 (NCO)/NiO core-shell nanowire arrays are deposited on nitrogen plasma-treated CC (NCC) to fabricate the ultrahigh stable SC. An ultrathin layer of NiO deposited on the NCO nanowire arrays via conformal ALD plays a vital role in stabilizing the NCO nanowires for thousands of electrochemical cycles. The optimized NCC/NCO/NiO core-shell electrode exhibits a high specific capacitance of 2439 F g-1 with a remarkable cycling stability (94.2% over 20 000 cycles). Benefiting from these integrated merits, the foldable solid-state SCs are fabricated with excellent NCC/NCO/NiO core-shell nanowire array electrodes. The fabricated SC device delivers a high energy density of 72.32 Wh kg-1 at a specific capacitance of 578 F g-1 , with ultrasmall capacitance decline rate of 0.0003% per cycle over 10 000 charge-discharge cycles. Overall, this strategy offers a new avenue for developing a new-generation high-energy, ultrahigh stable supercapacitor for real-life applications.

Hydrothermal Synthesis of NiCo<sub>2</sub>O<sub>4</sub> Nanowires on Carbon Fiber Paper for Hydrogen Evolution Catalyst

Nickel cobaltite (NiCo2O4) nanowires were successfully grown on the surface of carbon fiber via hydrothermal treatment, followed by annealing. After 2 h, SEM revealed the formation of NiCo2O4 nanowire arrays on the surface of the carbon fiber paper. With increasing hydrothermal time from 2 to 12 h, the NiCo2O4 nanowires also self-assembled into urchin-like morphologies. When used as catalysts for hydrogen evolution reaction, the NiCo2O4 nanowires exhibit an onset potential for the cathodic current at-0.13 V vs. Ag/AgCl in 0.1 M KOH.

Construction of NiCo2O4@NiFe LDHs core/shell nanowires array on carbon cloth for flexible, high-performance pseudocapacitor electrodes

NiFe layered double hydroxides (LDHs), a class of ionic layered compounds with high electrochemical activity, possess great potential in the field of pseudocapacitive energy storage. However, the practical applications of NiFe LDHs in supercapacitors are largely hindered by their inherently poor cycling life and low electrical conductivity. In this work, NiFe LDHs electrodeposited on mesoporous and conductive NiCo2O4 nanowire arrays that are grown on flexible carbon cloth, are investigated as active materials for pseudocapacitive application. This rational core/shell electrode design promises high specific surface area, shorten electron and ion transport distance for the enhancement of electrochemical kinetics. As such, a high specific capacitance (1.9 F cm−2 at 1 A cm−2, and 1160 F g−1 at 1 A g−1), excellent rate capability (83% retention as the current density was increased from 1 A cm−2 to 20 A cm−2), decent cycling stability (79% retention after 1000 charging/discharging cycles), and good flexibility have been obtained, implying their potential application as energy storage devices for flexible electronics.